The present invention relates to a fuel cell power generation system and a method for powering an electric vehicle.
Development of the electric vehicle has recently undergone increased activity in an effort to reduce air pollution and conserve fuel resources. A major stumbling block in the development of electric vehicles has been developing a suitable means of supplying power for the electrical drive motors. In most instances, the power has been supplied from a battery source. However, the current battery technology is not capable of supplying a sufficient amount of energy to power the vehicle over extended distances.
Fuel cells have recently been examined as an alternative power source for electrical vehicles. A fuel cell is a demand-type power system in which the fuel cell operates in response to the load imposed across the fuel cell. Typically, a liquid hydrogen-containing fuel (e.g., gasoline, methanol, diesel, naphtha, etc.) serves as the fuel supply for the fuel cell once converted to a gaseous stream that contains hydrogen. This is accomplished when the hydrogen-containing fuel is passed through a fuel reformer to convert the liquid fuel to a hydrogen gas (20-75% depending on the liquid fuel) that usually contains other passivating gas species such as carbon monoxide, carbon dioxide, methane, water vapor, oxygen, nitrogen, unburned fuel and, in some cases, hydrogen sulfide. The hydrogen is then used by the fuel cell as a fuel. An oxidant, usually air, is also supplied to the fuel cell to react with the hydrogen fuel to produce electric current. The electric current can then be drawn on demand in response to loads across the fuel cell to power electrical devices, such as an electric motor of an electric vehicle.
The invention disclosed herein will identify solutions to the following deficiencies in prior art systems:
(1) startup time;
(2) fuel cell system size and cost;
(3) reformer system size and cost;
(4) transient response time of the reformer; and
(5) elimination of passivating gas species damaging the fuel cell.
In most prior art systems, the DC load on the fuel cell is sensed and hydrogen and oxidant are supplied to the fuel cell to meet the demand upon the fuel cell. The problem associated with these prior art fuel cell systems is that while the response time of the fuel cell to changes in the load is theoretically essentially instantaneous, the response time of the processor in the flow of the liquid fuel to the reformer and the hydrogen from the reformer to the fuel cell is too time-consuming to meet the changing load requirements on the fuel cell. Thus, the fuel cell does not perform acceptably during large power demand instances. Furthermore, the reactions that take place required to release hydrogen from carbon form carbon dioxide and carbon monoxide (a fuel cell poison). During transient operation, a typical fuel reformer will allow unacceptable carbon monoxide levels through to the fuel cell causing potential failure of the system.
Moreover, another problem that faces liquid-fueled (reformers) fuel cell power systems in electric vehicles is that the fuel cell power system takes much longer (xcx9c1 minute) to start up than conventional vehicle systems (xcx9c3 seconds). In prior art systems, the reformer will not deliver usable hydrogen to the fuel cell until the operating temperature is reached, or nearly reached. This delay results in customer dissatisfaction with their product. Furthermore, this startup period is most susceptible to transient chemistry yielding much greater carbon monoxide levels than is acceptable, further delaying good response from the fuel cell (carbon monoxide poisoning gets much worse as the fuel cell nears ambient temperature as in startup conditions).
Moreover, another problem that faces liquid-fueled fuel cell power systems in electric vehicles is that the fuel cell power systems are relatively larger heavy and expensive. This is due in part to the existence of contaminants and diluents (i.e., non-hydrogen gases) in the hydrogen fuel provided to the fuel cell. These contaminants and diluents cause a relatively significant reduction in the power production per unit weight and volume of the fuel cell.
Accordingly, it would be desirable to provide a fuel cell power generation system for an electric vehicle which responds essentially instantaneously to large power demands without concern over carbon monoxide and other harmful gases, and is able to start up an electric vehicle engine in less than about three seconds.
It would also be further desirable to be able to provide a fuel cell power generation system which is lighter, smaller and more economical than other fuel cell power generation systems currently used for powering electric vehicles.
The present invention relates to a fuel cell power generation system for powering an electric vehicle. The system comprises a low temperature fuel cell, a reactor comprising a reformer for converting hydrogen-containing fuel into a reformate stream, and a metal membrane separator.
The reformate stream comprises a hydrogen gas stream. The metal membrane separator is capable of separating the hydrogen gas stream from the reformate stream. The fuel cell power generation system also includes a metal hydride buffer. The metal hybrid buffer is in line between the fuel cell and the membrane separator. The metal hydride buffer is capable of selectively storing hydrogen from the hydrogen gas stream and releasing the hydrogen.
The present invention also relates to a method for operating an electric vehicle powered by a fuel cell power generation system comprising a low temperature fuel cell, a reactor comprising a reformer, a metal membrane separator, and a metal hydride buffer, in line between the fuel cell and the membrane separator. The method comprises supplying hydrogen-containing fuel to the reformer, and converting hydrogen-containing fuel in the reformer to a reformate gas comprising a hydrogen gas stream and a by-product gas stream. The hydrogen gas stream is directed through the metal membrane separator to separate the hydrogen gas stream from the by-product gas stream, and the hydrogen gas is directed to the fuel cell to supply fuel to the fuel cell.
The present invention provides a fuel cell power generation system which, relative to prior art systems, reduces engine startup time, fuel cell system size and cost, reformer system size and cost, and transient response time of the reformer as well as eliminates the damage to the fuel cell from passivating gas species such as carbon monoxide and hydrogen sulfide.